Speech recognition systems are used in a wide variety of applications, and typically involve an input subsystem (e.g., one or more microphones) for obtaining the speech signals and a speech recognition subsystem, for determining the words that most likely correspond to the signals received. At times, speech recognition systems also include a separate directional subsystem for analyzing the signals received to determine the angle from which a signal originated. The quality of each of these subsystems and the interaction among them helps determine the quality and effectiveness of the speech recognition system.
Frequently, it is desirable to restrict the angle within which a microphone accepts input from a sound source. For example, the speech recognition system may be used to permit an operator to control a machine or other device by issuing spoken commands. In such instances, which are becoming more and more common, it can be important to accept spoken commands only from the operator, and to ignore speech or other sounds emanating from a direction other than that of the operator.
While a directional subsystem can be used to refine the analysis performed by the speech recognition subsystem, it also adds an extra level of cost and complexity. Signals from many angles are still received and analyzed by such microphones so that signals from undesired angles must still be detected and rejected.
Alternatively, a microphone with a narrow acceptance angle could be used. However, the design of such a microphone is complex, and its cost is significantly greater than the cost of a simple microphone. In addition, microphones with a narrow acceptance angle typically are larger than simple microphones, and can be too cumbersome to be useful for many applications in which a narrow acceptance angle is desired but space for the microphone is limited.
The present invention overcomes these and other problems with a system that provides a narrow acceptance angle without the use of complex microphones or a complex directional analysis subsystem, as will be shown in the remainder of the specification, referring to the attached drawings.